The growing search for new materials for orthopedic or reconstruction surgery, lead to the development, in the last two decades, of biomedical devices based on ceramics, such as hydroxyapatite and tricalcium phosphate. These ceramic materials were recognized as biocompatible and as having an osseoconductive behavior, and were thus used for the repair or replacement of bone defects.
Aiming a controlled porosity of these materials while keeping satisfactory mechanical properties, remains the technical challenge of these biomaterials. Efforts in manufacturing porous ceramics with interconnected pores have been made in order to enhance tissue growth. It is known that a porous and interconnected structure allows new tissue to penetrate the substrate, and stimulates the growth of new bone tissue.
For example, WO2009/053835, as well as a number of the prior art documents in the field, reports a method to make biomedical devices with controlled porosity, involving the replication in ceramics of 3D-substrates such as polymeric substrates, which are eliminated at the end of the process by sintering. This method has the disadvantage of necessitating several steps, first for the manufacture of the substrate and second for the elimination/release of the substrate. Furthermore, the release of the substrate is susceptible to result in cracking phenomena on the thin walls of the piece. To avoid these drawbacks, additives are used. Most of the time, these additives are not biocompatible. Moreover, there is a remaining high risk that the step of elimination of the substrate may cause a distortion in the work piece due to variations of the dimensions during the warm-up. For these reasons, elimination of the substrate may be a hazardous step that the present invention intends to avoid.
The present invention is thus advantageous, in that the process of the invention involves direct laser treatment of the powder without use of a substrate, which is time effective, avoids the risk of distortion of the work piece, and is free of additives. Consequently, the product resulting from the manufacturing process of the invention is also free of additives.
Some prior art documents related to ceramic devices avoid the use of polymeric substrates and directly mix powders, such as for example, U.S. patent application 20070210493. This U.S. patent application reports the manufacture of porous ceramics based on slurry prepared from by mixing alumina particles, glass frit, silica particles, silica sol and water. This mixture is set in a plate, dried and sintered in order to obtain a hard and resistant ceramic. However, this method leads to a filter for filtering fluid such as liquid and gas or the like, and is not adapted for a biomedical device.
Further prior art relates to methods of manufacturing three-dimensional objects by laser technology. U.S. Pat. No. 4,863,538 for example, reports how to make a three-dimensional objet from a powder of plastic, metal, polymer, ceramic powders, or composite materials. The reported method is a layer-wise method: the powder is dispensed into a target area where the laser selectively sinters the powder to produce a sintered layer; the layers are joined together until the completed part is formed.